The general goal of this project is to elucidate the mechanisms by which rubella virus establishes a persistent infection in vitro. Persistently-infected Vero cells have been established and cloned. A low percentage of the cells in these clones produce infectious virus, however, virtually all of the cells contain viral antigen. The persistent state could not be cured by growing these cells in the presence of rubella virus specific antibody. The mechanism which controls the production of infectious virus is under investigation. Since the clones were established from single cells, the viral genome must be replicated and passed to each daughter cell at mitosis. Emphasis, therefore, will be focused on elucidating the physical state and control of the rubella genome in the persistently infected cells. It is anticipated either that the genome may be maintained as a complementary DNA copy, or that it may be replicated under host cell control. Rubella virus released from the persistently-infected cells will be evaluated for temperature-sensitivity and for defective-interfering particles. This virus also will be subjected to acrylamide gel electrophoresis to determine the protein profile.